In the wake of the Great Depression, the Federal government created new institutions, including the Home Owners’ Loan Corporation (HOLC), to stabilize housing markets. As part of that effort, the HOLC created residential security maps for over 200 cities to grade the riskiness of lending to neighborhoods. Hartley and his co-authors trace the effects of these maps over the course of the 20th and into the early 21st century, focusing on the difference in outcomes (segregation, home ownership, house values, and credit scores) between residents living on a lower-graded side versus a higher-graded side of an HOLC boundary.